python.org is not specific to CPython, but I agree with Antoine that docs.python.org/devguide is.  So I went and found the blog post that Frank alludes to in the OP is here: http://fwierzbicki.blogspot.com/2011/11/contributing-to-jython.html
Nick proposed adding a jython page to the cpython devguide and Frank agreed, saying “much of a dev guide I might put up would largely cut and paste from there”.  If Jython development is very much like CPython’s apart from repo URI, build process and bug tracker URI, then it could fit in just one page and be part of the devguide.  If the process widely differs and many pages would be needed, then separate devguides may be better.